To extract smoke, dust and particles from welding places such places normally are provided with some kind of local extraction device. Said local extraction devices normally are provided with a plurality of movable, rods and/or rigid tube sections that are mutually pivoted, and provided with intermediate hose sections.
Preferably said device is attached to a wall or the ceiling where probably also a connection is made to a main line for the extraction of air. In embodiments utilizing a main line there is normally provided a central exhausting device. In some cases there is also provided at each extraction device a separate exhausting device.
The air extracted from the extracting spot is contaminated with smoke, dust and particles. To prevent such contamination from the environment the extracted air has to be cleaned somehow, before it is returned to the ambient air. To accomplish the cleaning of air extracted from the extraction spot it is previously known from the first case described above to complete said central exhausting device with a central filter apparatus. One embodiment of a filter is known from for instance GB 1329844. The device according to said patent comprises a separation chamber and a filter provided in said chamber. Similar embodiments are known also for systems using a central exhausting device.
Previously known types of filter devices to be used within the present technical field are comparatively complicated and normally expensive. When a filter is changed in a central filter device it is necessary to turn off completely the central exhausting device, and thereby all working sites connecting thereto will lack the evacuation of air during the time of exchange. The filter must also be dimensioned according to the type of contamination that requires the highest level of filter capacity. This may effect the actual costs for the filter apparatus in a most adverse way if only one or a few working sites will produce this type of contaminations.